1. Field of the Invention
This invention relates to a method of encrypting information, a method of decrypting information, an apparatus for encrypting information, and an apparatus for decrypting information.
Furthermore, this invention relates to an information recording medium.
2. Description of the Related Art
Japanese patent application publication number 10-269289/1998 discloses a system for managing the distribution of digital contents. In the system of Japanese application 10-269289, a distributor side encrypts and compresses digital contents into processing-resultant digital contents. The distributor side transmits the processing-resultant digital contents, an encryption-resultant contents key, and encryption-resultant accounting information to a communication opposite party. The distributor side implements a process of receiving a charge on the basis of contents use information transmitted from the communication opposite party. Then, the distributor side implements a process of dividing the received charge among interested persons including a copyright holder of the digital contents. On the other hand, a user side (a digital contents player) decrypts and expands the processing-resultant digital contents in response to the contents key, thereby reproducing the original digital contents. The user side subjects the accounting information to a reducing process responsive to the use of the digital contents. The user side transmits the reduced accounting information and the contents use information to the distributor side.
In the system of Japanese application 10-269289, a third person can illegally reproduce the original digital contents when getting the original contents key.
Japanese patent application publication number 10-283268/1998 discloses a system in which a recording medium stores encryption-resultant main information, and also encryption-resultant information representing a key for decrypting the encryption-resultant main information. Non-encrypted information representing conditions of decrypting the encryption-resultant main information is added to the encryption-resultant key information. In more detail, the encryption-resultant key information has non-encrypted control information which contains device information and region information. The control information is designed to prevent the encryption-resultant main information from being copied onto a magnetic recording medium or an optical disc in a user side for illegal use thereof.
The system of Japanese application 10-283268 has a problem as follows. The non-encrypted control information in the encryption-resultant key information can easily be altered by a third person. The alteration of the non-encrypted control information enables the third person to illegally copy the encryption-resultant main information.
Japanese patent application publication number 7-140896/1995 discloses first and second systems each for encrypting an ordinary text file. In the first system of Japanese application 7-140896, the ordinary text file is divided into ordinary text blocks each having the smallest limit of a data size range in which data can be transmitted between a disk buffer and an on-memory data area used by an application program. The ordinary text blocks are encrypted into encryption-resultant text blocks in response to a user key. The encryption-resultant text blocks are connected to form an encryption-resultant text file.
In the second system of Japanese application 7-140896, the ordinary text file is divided into ordinary text blocks each having the smallest limit of a data size range in which data can be transmitted between a disk buffer and an on-memory data area used by an application program. Data keys are generated from a user key and values peculiar to the respective ordinary text blocks. The total number of data keys is equal to that of the ordinary text blocks. The values of the offsets of the ordinary text blocks from the head of the ordinary text file are used as the peculiar values, respectively. The ordinary text blocks are encrypted into encryption-resultant text blocks in response to the data keys, respectively. The encryption-resultant text blocks are connected to form an encryption-resultant text file.
The first and second systems of Japanese application 7-140896 tend to be insufficient in security.